Buttons with plastics heads are in extensive use for ornamental effects of the head designs as well as for fastening purposes. Of these buttons, some types are known which combine a plastics head with a metallic leg piece. Varied means for joining the head and the leg piece are available according to the kinds of the plastics, but none of them thus far provided have proved fully satisfactory.
FIGS. 1 to 3 illustrate an example of the prior art using a thermosetting resin. A metallic leg piece as shown in FIGS. 1 and 2, which consists of an annular base 1 having upright legs (in this case, prongs with pointed tips) 2 with which the button is to be secured to a garment, is placed, together with a thermosetting resin, into a mold 3 and jointed integrally by thermally setting the resin to form a button head 4. In order that the leg piece can be securely embedded in the plastics head, its base 1 is annularly shaped to permit the resin to cover it completely. The button head of thermosetting resin is so hard that it is rarely scratched and permits sophisticated designs. When the button head 4 is placed in the cavity of a fitting die for attachment to a garment and a sufficient pressure for attachment is applied to the legs 2, localized forces will be exerted on the annular base 1 and hence on the button head 4, often causing cracks in the head and making the button defective. Indirectly responsible for the cracking are internal stresses that arise from the difference in thermal shrinkage coefficients between the button head and the leg piece upon the thermosetting treatment and cooling. FIGS. 4 and 5 show another conventional button which uses a rigid thermoplastic resin. A leg (in this instance a tubular stem) having a conically flaring end is inserted into a button head 6 having a recess 5 with a correspondingly spread botton. The leg is pressed in the direction of the arrow to expand the conical end so that, as shown in FIG. 5, the flaring end is flattened solidly against the spread bottom of the recess 5 to form a button. For this application a thermoplastic resin is usually used because a button head of a thermosetting resin tends to crack unless the dimensions are strictly controlled to exacting tolerance. However, a thermoplastic resin button head is not aethetically attractive, is easy to scratch or damage, and lacks resistance to heat and chemicals. FIGS. 6 and 7 illustrate a further conventional button which consists of a leg piece 11 fitted at its base flange into a recess 8 surrounded by a circular ridge 9 of a button head 10 of a rigid thermoplastic resin (FIG. 6), with the ridge 9 crimped flat against the flange (FIG. 7). The button head of this design can be made solely of a thermoplastic resin as the ridge 9 is deformed.